﻿156 
  

  

  Dr. 
  W. 
  Huggins 
  on 
  the 
  

  

  [Jan. 
  7, 
  

  

  relative 
  motion 
  of 
  approach 
  of 
  the 
  comet 
  and 
  the 
  earth 
  of 
  about 
  40 
  

   miles 
  per 
  second, 
  a 
  velocity 
  nearly 
  double 
  that 
  of 
  their 
  actual 
  relative 
  

   motion. 
  

  

  According 
  to 
  a 
  table 
  of 
  the 
  comet's 
  motion, 
  kindly 
  furnished 
  to 
  me 
  by 
  

   Mr. 
  Hind, 
  F.R.S.,the 
  comet 
  was 
  approaching 
  the 
  earth 
  on 
  that 
  day 
  with 
  

   a 
  velocity 
  of 
  about 
  24 
  miles 
  per 
  second. 
  The 
  part 
  of 
  the 
  earth's 
  orbital 
  

   motion 
  in 
  the 
  direction 
  of 
  the 
  comet 
  may 
  be 
  disregarded, 
  as 
  it 
  was 
  less 
  

   than 
  a 
  mile 
  per 
  second. 
  

  

  In 
  the 
  foregoing 
  observations 
  the 
  slit 
  was 
  placed 
  on 
  the 
  brightest 
  part 
  

   of 
  the 
  envelope, 
  close 
  in 
  front 
  of 
  the 
  nucleus. 
  Was 
  any 
  part 
  of 
  the 
  

   shift 
  due 
  to 
  the 
  motion 
  of 
  the 
  matter 
  within 
  the 
  comet 
  ? 
  If 
  the 
  mea- 
  

   sures 
  taken 
  on 
  July 
  8, 
  when 
  the 
  lens 
  was 
  found 
  to 
  have 
  shifted, 
  could 
  

   be 
  regarded 
  as 
  trustworthy, 
  they 
  would 
  indicate 
  a 
  slightly 
  larger 
  shift 
  on 
  

   that 
  day. 
  

  

  In 
  connexion 
  with 
  the 
  question 
  whether 
  the 
  bright 
  bands 
  were 
  fur- 
  

   nished 
  by 
  a 
  vapour 
  containing 
  carbon 
  in 
  some 
  form, 
  it 
  is 
  of 
  importance 
  

   to 
  notice 
  that 
  the 
  bright 
  line 
  near 
  G- 
  which 
  accompanies 
  the 
  three 
  bands 
  

   in 
  the 
  spectrum 
  of 
  carbon 
  and 
  its 
  compounds 
  appears 
  to 
  be 
  absent 
  in 
  the 
  

   spectrum 
  of 
  the 
  comet. 
  I 
  took 
  some 
  pains 
  to 
  satisfy 
  myself 
  that 
  this 
  line 
  

   was 
  not 
  to 
  be 
  detected 
  in 
  the 
  comet's 
  spectrum. 
  If 
  it 
  had 
  been 
  present 
  

   with 
  the 
  same 
  relative 
  brilliancy 
  which 
  it 
  possesses 
  in 
  the 
  terrestrial 
  

   spectrum, 
  I 
  should 
  have 
  been 
  able 
  to 
  see 
  it 
  easily. 
  The 
  relative 
  faint- 
  

   ness 
  or 
  entire 
  absence 
  of 
  this 
  more-refrangible 
  band 
  might 
  find 
  its 
  

   explanation 
  possibly 
  in 
  the 
  low 
  temperature 
  of 
  the 
  cometary 
  matter. 
  

  

  If 
  the 
  bands 
  are 
  to 
  be 
  considered 
  as 
  due 
  to 
  carbon, 
  we 
  have 
  to 
  inquire 
  

   in 
  what 
  form 
  the 
  carbon 
  exists 
  in 
  the 
  matter 
  of 
  the 
  comet. 
  In 
  my 
  paper 
  

   on 
  Comet 
  II., 
  1868, 
  I 
  pointed 
  out 
  that 
  though 
  some 
  comets 
  have 
  been 
  

   exposed 
  to 
  an 
  intense 
  degree 
  of 
  solar 
  radiation, 
  and 
  though 
  carbon 
  might 
  

   exist 
  possibly 
  in 
  some 
  condition 
  more 
  easily 
  volatilized 
  thau 
  those 
  with 
  

   which 
  we 
  are 
  acquainted 
  on 
  the 
  earth, 
  " 
  still, 
  under 
  the 
  most 
  favourable 
  

   of 
  known 
  conditions, 
  the 
  solar 
  heat 
  to 
  which 
  the 
  majority 
  of 
  comets 
  are 
  

   subjected 
  would 
  seem 
  to 
  be 
  inadequate 
  to 
  the 
  production 
  of 
  luminous 
  

   vapour 
  of 
  carbon." 
  I 
  then 
  stated 
  that 
  the 
  necessity 
  for 
  a 
  very 
  high 
  tem- 
  

   perature 
  would 
  be 
  diminished 
  if 
  we 
  were 
  to 
  conceive 
  of 
  the 
  existence 
  in 
  

   the 
  comet 
  of 
  a 
  compound 
  of 
  carbon 
  and 
  hydrogen 
  which 
  could 
  furnish 
  

   those 
  bands 
  without 
  undergoing 
  decomposition. 
  

  

  The 
  remarkable 
  connexion 
  of 
  the 
  orbits 
  of 
  comets 
  with 
  those 
  of 
  swarms 
  

   of 
  meteors, 
  together 
  with 
  the 
  presence 
  of 
  hydrocarbons 
  in 
  many 
  

   meteorites, 
  would 
  seem 
  to 
  suggest 
  the 
  probability 
  that, 
  if 
  carbon 
  be 
  present 
  

   in 
  comets, 
  it 
  exists 
  in 
  combination 
  with 
  hydrogen. 
  

  

  I 
  stated, 
  in 
  the 
  paper 
  quoted 
  above, 
  that 
  the 
  spectrum 
  of 
  bright 
  bands 
  

   was 
  also 
  obtained 
  from 
  cyanogen. 
  In 
  the 
  case 
  of 
  the 
  hydrocarbons, 
  the 
  

   spectrum 
  of 
  bands 
  was 
  accompanied 
  by 
  the 
  lines 
  of 
  hydrogen 
  ; 
  and 
  when 
  

   cyanogen 
  was 
  employed, 
  the 
  known 
  complex 
  spectrum 
  of 
  nitrogen 
  was 
  

   present. 
  A 
  spectrum 
  essentially 
  the 
  same, 
  but 
  less 
  complete, 
  was 
  

  

  